Sensors, for measuring the throughput of crops and based on different physical principles, are used in harvesting machines for indicating the yield and/or for yield mapping. The sensors measure the crop throughput within certain error tolerances. In many systems, throughputs below a certain threshold value can no longer be precisely measured. It is also conceivable, due to the error tolerances of the sensors, that throughputs are measured even though no crop is transported through the harvesting machine.
Harvesting machines are, as a rule, also provided with so-called hectare or acre counters or meters used to measure the harvested area. They continue to count a measuring value representing the worked surface if a number of conditions have been met, such as positive, i.e., forward, travel speed, front attachment in harvesting position, and if the crop processing and/or transport devices are in an operating mode. Since the presence of crop material is not checked, the harvested area continues to be counted even if no flow of crop material is actually present. Even given a logical linkage to the signals of the sensors for measuring the crop throughput, the corresponding information is not always correct, and results in incorrect area values.
The suggestion was therefore made to combine the sensor for measuring crop throughput with a sensor for detecting the presence of crop flow. To this end, U.S. Pat. No. 6,401,549, which corresponds to DE 199 03471 C uses a light barrier in the discharge device of a field chopper. A measured value different from zero for the crop flow is emitted only if it detects a crop flow. However, the light barrier requires an additional structural component whose parts coming in contact with the crop flow wear down and can become contaminated after being used for a rather long time.
Acoustic sensors are used in combines to detect lost grain. They detect oscillations caused by lost grain falling onto impact plates or rods.